computer Network

1. Computer Networking
(OSI Model-TCP/IP Model-Networking Device
Presented by:
Md.Shohel Rana
Lecturer, Dept. of CSE
ISTT UNIVERSITY

2. OBJECTIVES
 Understand the rationale for the existence of networks.
 Distinguish between the three types of networks: LANs, MANs, and WANs.
 Understand the OSI model and TCP/IP.
 List different connecting devices and the OSI layers in which each device operates.
 Understand client-server models.

3. Computer networks
 A computer network is a combination of systems connected through
transmission media.
Local area network (LAN)
Metropolitan area network (MAN)
Wide area network (WAN)

4. Model and protocol
A model is the specification set by a standards organization as a
guideline for designing networks.
A protocol is a set of rules that controls the interaction of
different devices in a network or an internetwork.

5. OSI MODEL
 The Open Systems Interconnection (OSI) model is a theoretical
model that shows how any two different systems can communicate
with each other.

6. Flow of data in the OSI model
Header
Header
Header
Trailer

7. Seven layers of OSI model
1. Physical layer
2. Data-link layer
3. Network layer
4. Transport layer
5. Session layer
6. Presentation
layer
7. Application layer

8. 1.Physical layer
 The physical layer is responsible
for transmitting a bit stream over a
physical medium.
 It encodes and decodes bits
into groups of bits.
 It then transforms a stream of bits
into a signal.

9. 2.Data-link layer
 The data-link layer organizes bits into
logical units called frames.
 The data-link layer is responsible only for
node-to-node delivery of the frame.
 The data-link layer is often
responsible for error handling
between two adjacent stations.

10. 3.Network layer
 The network layer is responsible for delivery of a packet
between the original source and final destination.
 Using logical addresses (IP addresses) instead
of physical addresses.
 Example of IP address
 140.122.76.121 (4 Bytes)

11. 4.Transport layer
 The transport layer is responsible for
source-to-destination delivery of the
entire message.
 The transport layer is responsible for
breaking the entire message into
several packets and delivery them to
the network layer.
 The transport layer is responsible
for ensuring that the whole
message is transmitted.
 If packets arrive out of order, they must
be reorganized.

12. 5. Session layer
 The session layer is designed to control the dialog
between users.
 The synchronization points divides a long
message into smaller ones and ensure that each
section is received and acknowledged by the
receiver.
 Most network implementations today do not use a
separate session layer, their services are usually
included in the application layer.

13. 6.Presentation layer
 The presentation layer is concerned with the syntax and
semantics of the information exchanged between two
systems.
 It deals with the fact that different systems use different
coding methods.
 Compress and decompress data
 Encrypt and decrypt data
 Most implementations do not use a presentation layer today,
their services are usually included
in other layer.

14. 7. Application layer
 The application layer enables the user to
access the network.
 It defines common applications that can
be implemented to make the job of the
user simpler.
 Will be discussed later…

15. Categories of networks

16. LANs

17. Local area network
 Bus topology
 When a station sends a frame to another
computer, all computer receiver the frame and
check its destination address.
 Star topology
 Hub (all, like a bus) v.s. switch (one)
 Ring topology
 When a computer needs to send a frame to
another computer, it sends it to its neighbor.

18. MAN

19. WAN

20. Wide area network
WAN is the connection of individual
computers or LANs over a large area.
A person using a telephone line to
connect to an ISP is using a WAN.
ISP: internet service provider

21. Connecting devices

22. Repeater
A repeater is an electronic device and operate
only in the physical layer of the OSI model.
A repeater can regenerate the signal and send
it to the rest of the network.

23. Note:
Repeaters operate at the first layer
(physical layer) of the
OSI model.

24. Bridge

25. Bridges
 In bus topology, a bridge is a
traffic controller.
 It can divide a long bus into
smaller segments so that each
segment is independent
trafficwise.
 The bridge uses a table to decide if
the frame needs to be forwarded to
another segment.
 With a bridge, two or more pairs of
stations can communicate at the same
time.

26. Note:
Bridges operate at the first two
layers
(physical layer and data-link layer)
of the OSI model.

27. Switch—one kind of dynamic bridge

28. Routers in an internet

29. Note:
Routers operate at the first three
layers
(physical, data-link, and network
layer)
of the OSI model.

30. Routers
Whereas a bridge filters a frame based
on the physical address of the frame, a
router routes a packet based on the
logical address of the packet.
Whereas a bridge may connect two
segments of a LAN, a router can connect
two independent networks.

31. Gateways
A gateway is a connecting device that
acts as a protocol converter.
A gateway is usually a computer installed
with the necessary software.
Today the term gateway is used
interchangeably with the term router. The
distinction between the two terms is
disappearing.

32. Connecting devices and the OSI model

33. Protocols
TCP: Transmission control protocol
UDP: User datagram protocol
IP: Internet protocol
FTP: File transfer protocol
SMTP: Simple mail transfer protocol
POP: Post office protocol
HTTP: Hypertext transfer protocol

34. TCP/IP and OSI model

35. IP addresses in dotted-decimal notation
Network layer

36. Application layer
Client-server model

37. Client-server model
Client: an application program running on
a local machine
Server: an application program running
on a remote machine
A client requests a service from a server.
The server program is always running,
and the client program runs only when
needed.

38. FTP
FTP -- Client-server model

39. FTP -- Client-server model
FTP was designed to resolve two
problems:
Different coding systems in use
One machine may use ASCII, and other may use
Unicode
Different file formats in use

40. SMTP -- Client-server
model
SMTP/POP

41. Email address
Shohel_CSEistt.edu.bd

42. TELNET-- a general client-server model
Local login v.s. remote login
TELNET is a general client-server program on
the Internet that allow remote login

43. HTTP
 URL
 http://www.istt.com
ftp://140.122.77.121
 URL: Uniform resource locator
 A special kind of addressing using by HTTP

44. WWW
WWW: World wide web
Hypertext: home page
Browser
Document Types
Static documents
Dynamic documents
Active documents

45. Browser

46. Categories of Web documents
Static documents
HTML: Hypertext Markup Language
Dynamic documents
CGI: Common Gateway Interface (Perl)
Active documents
Java language